1. Field of the Invention
The present invention relates in general to a technical field of a portable communication terminal such as a mobile telephone. In particular, the invention relates to a technical field of a portable communication terminal equipped with a camera.
2. Description of the Related Art
Heretofore, in a portable communication terminal such as a mobile telephone, in general, in order to pursue enhancement of portability, a miniature battery is forced to be used therein. For this reason, in a conventional portable communication terminal, in order to realize low power consumption, there is adopted an operation control method including carrying out intermittent reception during standby reception.
When in the portable communication terminal for which such an operation control method is adopted, a necessary communication protocol processing is executed between the portable communication terminal and a base station during call or packet communication, a radio communication unit or a control unit for a communication processing is operated. On the other hand, this portable communication terminal, during the standby operation, makes transition to an intermittent reception mode, and also for the purpose of mainly maintaining reception synchronization, carries out a reception operation once for one super-frame (e.g., about 720 ms) in the intermittent reception mode. Then, the portable communication terminal complying with such an operation control method carries out the intermittent operation for power-down of a radio communication unit, a central processing unit (CPU) and the like for a time period other than a time period for one reception operation in the intermittent reception mode to reduce the power consumption.
As an example of a portable communication terminal of such an operation control method, in recent years, a mobile telephone equipped with a camera (image pickup device) has remarkably come into wide use in the field of the mobile telephone. Then, in a case where using the camera function as well as the radio communication function, when it is unnecessary to operate the radio communication unit and the CPU, an operation mode of such a mobile telephone with a camera is set to the intermittent reception mode.
The camera installed in such a mobile telephone is a camera adapted to execute an image processing with respect to digital signals (hereinafter referred to as “a digital camera” for short when applicable). In general, many digital cameras are several tens of MHz in frequency of an operation clock signal. Then, an image data signal outputted from such a digital camera becomes a signal having a frequency corresponding to the frequency of the operation clock signal.
Here, let us consider a case where in the mobile telephone with a camera operated in accordance with such an operation clock signal, the camera is used during the standby in the intermittent reception mode. In this case, the mobile telephone with a camera restarts a reception operation at a predetermined timing. As for a problem encountered in restarting the reception operation, the mobile telephone with a camera has a problem in that high frequency components of an output signal of the camera in operation before restart of the reception operation are radiated from a camera body, a signal wiring pattern on a circuit board, an IC for an image processing, and the like. This radiation becomes a cause of deterioration in reception sensitivity since the radiation brings about an increase in noise for a radio communication unit.
As measures against such a problem due to the high frequency signals, various methods including coping with such a problem have been proposed for the conventional mobile telephone with a camera. More specifically, for such a mobile telephone with a camera, there have been proposed a method including providing a bypass capacitor within a control circuit, a method including suitably changing a design of a wiring pattern on a circuit board, a method including strengthening GND (earth) of a circuit board, and the like.
However, in a case where a circuit as a measure for preventing an adverse effect due to the high frequency signals is provided in the mobile telephone with a camera, there are caused an increase in the number of components or parts and reduction in the degree of freedom in mounting of a circuit board. In general, the mobile telephone with a camera is limited in miniaturization and lightening as compared with a mobile telephone equipped with no camera. However, from the general market request, for a portable communication terminal such as a mobile telephone, portability is regarded as important. For this reason, the installation of the circuit as a measure for the above-mentioned problem which obstructs miniaturization and lightening becomes a serious program from a viewpoint as well of convenience and salability of the mobile telephone with a camera.
Then, in JP 2002-261880 A, there is proposed a mobile telephone with a camera in which the above-mentioned problem due to the high frequency signals caused along with the intermittent reception operation is taken into consideration.
That is, JP 2002-261880 A proposes a technique in which an operation clock signal for a camera is stopped for a time period when a mobile telephone with a camera is operated in an intermittent reception mode, the time period containing a reception slot during an standby reception operation.
More specifically, in the mobile telephone described in JP 2002-261880 A, the camera is operated in accordance with the operation clock signal only for a time period of one frame (about 30 ms) right after an end timing of the reception slot during a super-frame (e.g., 720 ms). On the other hand, in this mobile telephone, the camera operation clock signal is stopped for other time periods. Here, other time periods concerned are expressed as follows.
                              super          -                      frame            ⁢                                                  ⁢                          (                              720                ⁢                                                                  ⁢                ms                            )                                -                      reception            ⁢                                                  ⁢            slot            ⁢                                                  ⁢                          (                              6.6                ⁢                                                                  ⁢                ms                            )                                -                      1            ⁢                                                  ⁢            frame            ⁢                                                  ⁢                          (                              30                ⁢                                                                  ⁢                ms                            )                                      =                  683.4          ⁢                                          ⁢          ms                                    (        1        )            
In the mobile telephone described in JP 2002-261880 A, the camera is operated only for a time period of about 40 ms obtained by adding the reception slot in the super-frame to the time period of one frame right after the reception slot as expressed in Equation 1 to thereby generate image pick-up data. Thus, in such a mobile telephone, a problem is encountered in that when an image based on that image pickup data is displayed on a display unit, the displayed image is poor in visibility, and a user is therefore given a sense of incompatibility.
In addition, in the technique described in JP 2002-261880 A, the image pickup data for one frame is transferred from the camera to a control unit every super-frame. For this reason, a frame rate of the display unit is judged to become about 1.39 fps. Consequently, when a moving body is photographed with the mobile telephone with a camera operated as described above, likewise, the problem is still encountered in that the displayed image is poor in visibility.